1. Field of the Invention
The invention concerns a hydro-pneumatic tensioning unit, particularly for use on a tracked vehicle for pressing a guide wheel against the tensioned track.
2. Description of the Prior Art
There are numerous engineering applications of hydro-pneumatic tensioning units, particularly where there is a need for a rod which can yield when overloaded and can supply a restoring force when a load is removed. An example of an application is protection of a plowshare against overload damage when encountering large rocks in the soil. Another example is use in a mine prop when mining in areas subject to seismic disturbances. A mine prop in such a situation must be able to give way to some degree when subjected to a severe increase in ground pressure. Finally, hydro-pneumatic tensioning units are also commonly used for tensioning the tracks of tracked vehicles. They have the distinct advantage over mechanical-hydraulic or purely mechanical tensioning units (see, e.g., U.S. Pat. Nos. 2,315,421 and 2,561,901) that large forces can be developed with small available installation space, while the slope of the spring characteristic is kept low i.e., the spring constant is kept low. In addition, by simple changes in the pre-pressurization of the gas in the gas space it is possible to achieve different forces with the same installed masses. Known hydro-pneumatic tensioning devices (e.g., Ger AS No. 1,125,778 and Ger. Pat. No. 1,158,379) have complex structures and require a long length of space for insertion.
Where a piston is used as the separating member, there are the disadvantages that the piston must be furnished with dynamically loaded high pressure seals, the surrounding cylinder must be finely machined and dimensioned such that even at high pressure the cracks which may develop are not so great that they cannot be bridged by the high pressure seals, and it still is not possible to avoid leakage losses over time.
One may dispense with dynamically loaded high pressure seals if a bladder or diaphragm is used as the separating member, but such a device is accompanied by a complex and costly construction and an excessive length. The requirements in applications for overload protection for plows, or for tracked vehicles, are for a short structure, however.